On August 13, Trump dropped to 34% approval on Gallup
That places him in exclusive company. Obama never dropped that low, nor did Clinton, Ford or Reagan.
The only Presidents ever to drop below 34 were the Bushes, Truman, Nixon, and Carter.
Where Trump really stands out, however, is the height of his peak (or lack thereof). Every other US president has reached at least a 66 at some point, even Nixon. Trump has never topped 46. Because his peak is so modest, Trump's average approval rating is currently the lowest in history by a country mile. His average is below 40, while Truman and Carter were right around 45.